But the National Rifle Association and other gun-rights advocates paint a dark picture of expanding background checks to private purchases, insisting the move inevitably would lead to a national firearms registry.

With a registry in place, they say, the stage would be set for the NRA's worst nightmare - gun confiscations.

The background check proposal, part of a post-Newtown Senate package facing an uphill climb on Capitol Hill, is "aimed at one thing … registering your guns," said NRA CEO Wayne LaPierre in February. "When another tragic 'opportunity' presents itself, that registry will be used to confiscate your guns."

LaPierre himself circled back to the claim last Sunday on NBC's "Meet the Press," insisting "there will be a registry."

But apart from the political crossfire, some gun policy experts say they are baffled over the logic behind the pro-gun checks-registry-confiscation equation.

"Except as matter of fantasy, it's inconceivable; it would be laughable if it weren't so frightening," said Garen Wintemute, director of the Violence Prevention Research Program at the University of California, Davis.

Under the Brady law of 1993, gun sales by only federally licensed firearms dealers are subject to a check with the National Instant Criminal Background Check System operated by the FBI, which says that more than 100 million requests have been submitted in past decade, with more than 700,000 resulting in denials.

Schumer's legislation would widen background checks to include gun sales between individuals, including those at gun shows. Private parties would be required to have a licensed firearms dealer complete the sale with a background check.

Exceptions would be made for gifts between family members, temporary loans and, under certain circumstances, gun exchanges among hunters and at shooting ranges and competitions.

Current law requires the FBI within 24 hours to destroy background-check requests that result in approvals, although dealers keep a record of the check.

Schumer aides insist none of this would change under his proposal. The government would not possess background-check data with which to build a registry.

But a one-time Schumer ally on the Republican side, Sen. Tom Coburn, R-Okla., parted ways with the New York Democrat over firearms dealer background-check record-keeping, which Schumer supports and Coburn opposes.

David Kopel, an NRA member and research director at the Independence Institute in Denver who has testified before Congress on guns, said universal background checks would represent a "decentralized" database tantamount to a national registry.

"When you want to confiscate guns, you go to the gun dealers and get the records," he said.

He said the process could take decades to unfold.

"It's more like smoking and cancer … Smoking does hugely raise the risk of dying of cancer," Kopel said.

Kopel pointed to the United Kingdom, Canada and Australia, which he said all used gun registration and licensing as the basis for seizing weapons that were restricted in the wake of massacres comparable to the one at Sandy Hook Elementary School in Newtown, Conn., in which shooter Adam Lanza killed 20 children and six adults with an AR-15 semiautomatic rifle.

Some who follow the gun debates say a president or congressional leaders who push confiscation would do so at their political peril.

Fear of gun registration and confiscation "has been an NRA mantra forever," said William Vizzard, a criminal justice professor at California State University in Sacramento and formerly an ATF supervisor in San Francisco. "It's based on nothing but the fact they just keep saying it over and over again."

Gerald Nunziato, a former Bureau of Alcohol, Tobacco, Firearms and Explosives agent who directed the bureau's National Tracing Center from 1991 to 1998, said that under the 1934 National Firearms Act, the ATF is required to maintain a registry of machine guns, sawed-off shotguns, silencers and other weaponry favored by Prohibition-era gangsters.

"If what the NRA says is true, why haven't these weapons been seized?" Nunziato said.

Memo, buybacks

The NRA points to two "smoking guns." One is a Jan. 4 Justice Department memo, which says universal background check "effectiveness depends on the ability to reduce straw purchasing, requiring gun registration and an easy gun transfer process."

Elsewhere it says gun buybacks are ineffective "unless massive and coupled with a ban." The NRA used the memo in an ad campaign, with NRA lobbyist Chris Cox intoning: "Still think President Obama's proposals sound reasonable?"